This invention relates generally to conveyor diverting systems, and, more particularly, to conveyor diverting systems having an endless conveying surface composed of multiple surface members, each one or group of adjacent ones mounted with a laterally movable shoe capable of diverting articles from the conveyor by pushing laterally against the articles as they move down the conveyor. Such lateral pushing thereby diverts a package, such as from the main conveyor to an adjacent branch conveyor, or other receiving structure.
Article diverters using a moving conveying surface consisting of a plurality of parallel surface members mounted to endless chains have been known for a number of years. Such diverters utilize a diverter shoe movably mounted on each surface member for lateral movement with respect to the conveying surface under the guidance of a track network. The track network is located generally under the conveying surface and guides the diverter shoes via pins which descend from the diverter shoes and engage the track network. Diverting gates in the track network selectively transfer guidance of each diverter shoe from a track running in the direction of the movement of the conveying surface to a diagonal track, or plurality of diagonal tracks, in order to cause lateral movement of the diverter shoes. In order to avoid wasted spacing between variable-length packages, such diverters may include manual or automatic measuring means at an infeed point to cause the diverter gate associated with the selected branch conveyor to divert a selected number of shoes corresponding in general to the length of the package. Exemplary of this type of conveyor are U.S. Pat. No. 3,361,247, issued to James N. Lauzon et al. and U.S. Pat. No. 4,738,347, issued to Brouwer and commonly assigned with the present invention.
With increased demands for the number of packages to be conveyed by such conveying systems, the inter-package spacing distance has become a critical factor in the design of conveying systems. Decreasing the spacing between packages on the conveyor allows a greater throughput of packages by the conveyor. Conversely, providing more space between the packages results in a diminished efficiency and throughput.
Prior diverting systems have addressed the problem of reducing the inter-package spacing requirements. U.S. Pat. No. 5,038,912, issued to David Cotter and commonly assigned with the present application discloses a single diagonal diverting track that is located underneath the conveying surface and is oriented at an angle to the main conveyor and generally points in the direction of the branch conveyor. As packages move down the conveyor, sensors are used to determine the length of the package. When the package reaches the diverting area, a gate is activated which channels the guide pins of the diverting shoes to an alternate path defined by the diagonal diverting track. The diverting gate remains activated to sequentially divert so many diverting shoes as are necessary, based on the measured package length, to successfully push the package off the main conveyor and onto the branch conveyor. After enough diverting shoes have been diverted, the diverting gate is deactivated, and subsequent diverting shoes proceed along one side of the conveyor where they do not divert the adjacent traveling packages.
A specific minimum inter-package spacing is required in this system as a result of the rotation of the diverted package as it is initially diverted. Because of this rotation, additional inter-package spacing is required to avoid conflict between the diverting package and a closely trailing package. This rotation pushes the trailing corner of the package adjacent the branch conveyor back a distance, which can be estimated using the width (W) of the package and the acute angle (.theta.) which is formed by the intersection of the main conveyor and the branch conveyor. Using these two variables and assuming that the package rotates about the trailing corner opposite the branch conveyors, it will be observed that: EQU A=W sin .theta.
where A is the distance the trailing corner adjacent the branch conveyor is pushed back by the package's rotation. It is, therefore, necessary with this system that packages to be diverted are not spaced closer together than the distance W sin .theta..
By way of example, if a diverting branch is oriented at about 20.degree. with packages 16 inches in width, an inter package distance of approximately 5.5 inches is necessary. If the package is 24 inches long, this results in the need for approximately 23% more empty space on the conveyor. A hypothetical system that could divert packages without any significant space between packages could thus produce a 23% increase in package throughput without any increase in conveyor speed. The high desirability of such a system is thus clear.
Another method of diverting packages known, which reduces the required inter-package spacing, is described in commonly assigned U.S. Pat. No. 5,165,515, issued to Michael L. Nitschke et al., which is commonly assigned with the present application. This system increases throughput by not rotating the diverted packages. This non-rotation is accomplished by using a plurality of generally parallel diverting tracks oriented diagonally with respect to the direction of conveyor movement, instead of a single diverting track. Each track has its own diverting gate which is actuated to divert the movement of the diverting shoes from the direction of the conveyor to the lateral diverting direction. By simultaneously activating more than a single diverting gate, a group of diverting shoes corresponding to the measured package length can be moved laterally across the conveyor surface. This group of shoes acts along nearly the entire length of the package to be diverted and, therefore, causes no rotation of the package. Without rotation of the package, the inter-package spacing requirement is reduced to a minimum.
However, this technique is not without difficulties. The deliberate non-rotation of the packages means the packages will enter the branch conveyor still aligned parallel to the main conveyor, but oriented generally diagonally with respect to the branch conveyor (i.e., their lengthwise sides are not parallel to the direction of motion of the branch conveyor). This orientation significantly increases the necessary width of the branch conveyors, resulting in an increase in cost and a reduction in the spacing on branch conveyors. Another difficulty with this method is that it requires an array of diverting gates and associated diverting tracks which must be duplicated for each divert point which adds cost to the diverting system.
It will thus be observed that there exists a need for a conveyor diverting system that can divert packages with little or no inter-package spacing and ensure that packages diverted to the branch conveyor are properly aligned, all while keeping costs to a minimum.